1. Field of the Invention
The present invention relates to a method and system for forming an antenna pattern, and more particularly, to the field of beam forming circuitry for antennas.
2. Description of the Related Art
Many communication systems, such as wireless communication systems, radar systems, sonar systems and microphone arrays, use beam forming to enhance the transmission and/or reception of signals. In contrast to conventional communication systems that do not discriminate between signals based on the position of the signal source, beam-forming systems are characterized by the capability of enhancing the reception of signals generated from sources at specific locations relative to the system.
Generally, beam-forming systems include an array of spatially distributed sensor elements, such as antennas, sonar phones or microphones, and a data processing system for combining signals detected by the array. The data processor combines the signals to enhance the reception of signals from sources located at selected locations relative to the sensor elements. Essentially, the data processor xe2x80x9caimsxe2x80x9d the sensor array in the direction of the signal source.
U.S. Pat. No. 5,581,620 shows a corresponding signal processor that can dynamically determine the relative time delays between a plurality of frequency-dependent signals. The signal processor can adaptively generate a beam signal by aligning the plural frequency-dependent signals according to the relative time delays between the signals.
Within wireless communication systems, such as wireless mobile communication systems, directive antennas can be employed at base station sites as a means of increasing the signal level received by each mobile user relative to the level of received signal interference. This is effected by increasing the energy radiated to a desired recipient mobile user, while simultaneously reducing the interference energy radiated to other remote mobile users.
U.S. Pat. No. 6,101,399 shows a method for forming an adaptive phase array transmission beam pattern at a base station. This method relies on estimating the optimum transmit antenna beam pattern based on certain statistical properties of the received antenna array signals. The optimum transmit beam pattern is found by solving a quadratic optimization subject to quadratic constrains.
U.S. Pat. No. 6,011,513 shows a beam-forming circuitry utilizing PIN diodes. The PIN diode circuit arrangement comprises a digital-to-analog converter with a reference voltage controller arranged to vary the converter""s response to digital input signals to compensate for the PIN diodes non-linear response.
xe2x80x9cA digital adaptive beam forming QAM demodulator IC for high-bit-rate wireless communicationsxe2x80x9d J-Y Lee, H-C Liu and H. Samueli, IEEE Journal of Solid-State Circuits, March 1998, pp. 367-377, discloses a method for adaptive beam forming in conjunction with frequency hopping. By comparing the beam form data with a reference signal or a training sequence, the receiving pattern converges to the desired result, steering the main beam toward the target user while simultaneously placing nulls in the interferers"" directions. The applications for the transceiver include notebook computer communications, portable multimedia radios and nomadic computing in both cellular and peer-to-peer communication networks. The source directions are assumed unknown a priori. Further, the method features real-time tracking capability for the adaptive beam forming.
A common disadvantage of prior art beam forming methods and systems is the expenditure of a dedicated digital signal processing system which is used for the beam forming. This constrains applications of beam forming for consumer devices.
It is therefore an object of the invention to provide an improved method and electronic circuit for forming an antenna pattern.
It is a further object of the invention to provide a receiver and a transmitter featuring beam forming for application in consumer devices.
The invention provides a cost efficient method and electronic circuit for forming an antenna pattern. This allows for the implementation of beam forming for antennas in consumer devices, such as car-radio receivers with improved multi-path reception, mobile and wireless telephony devices such as GSM, DECT or blue tooth mobile devices with low cost transceivers having beam forming capabilities, as well as for space-time coding applications.
The beam forming capability in the receiver/transceiver system leads to improved RF performance. The basic principle of the beam forming relies on the availability of distinct RF signals coming (going) to two or more antennas. By selectively phase-shifting the RF signals with respect to each other, a programmable antenna pattern results.
For example, the antenna pattern can be adjusted with the objective of:
Cancelling multi-path interference caused by secondary transmission paths. The main lobe of the antenna pattern is adjusted in the direction of the direct reception path and the combined antennas gain in the direction of the reflected beams is minimized; and
Providing a means for the implementation of space-time diversity systems. By sending and receiving signals which are xe2x80x9cspatiallyxe2x80x9d coded, it is possible to have several devices operating on the same wavelength (e.g., in an office) without severe interference problems. Each transceiver adjusts its xe2x80x9cbeam directionxe2x80x9d to attain the RF link to a desired transceiver xe2x80x9cpartnerxe2x80x9d.
The invention is advantageous in that it enables implementing the beam forming in the analog domain. This way, the expenditure for digital multipliers and other digital signal processing steps are avoided. In a preferred embodiment, this is accomplished by adding a programmable control current to at least one of the branches of two phase-locked loops in order to produce the required phase shift of the antenna signals.